1. Field of the Invention
The present invention relates to a rolling bearing assembly having a lubricating function for lubricating a work machine spindle or the like with a grease.
2. Description of the Prior Art
The lubricating method for lubricating bearing assemblies for a spindle used in a work machine is well known, which includes a grease lubrication that can be utilized maintenance-free, an air oil lubrication for spraying a lubricant carrier air, mixed with a lubricant oil, into bearings through a nozzle, and a jet lubrication for jetting a lubricant oil directly into bearings. Machine tools used in these days are getting utilized in a high speed environment with an aim at increasing the processing efficiency and the air oil lubricating technique has come to be largely used as it can afford a relatively inexpensive and fast lubrication for the spindle bearings. However, this air oil lubricating technique requires the use of an air oil supplying equipment as an incidental equipment and is therefore considered involving such a problem as associated with cost, noise, energy saving and resource saving. In addition, the air oil lubricating technique involves an additional problem in that the environment may be contaminated as a result of scattering of oil used therein. In order to alleviate these problems, a high speed orientation through the use of the grease lubrication is recently getting highlighted and is increasingly desired for.
Since the grease lubrication is accomplished solely with a grease filled during assemblage of the bearing assembly, it is considered that a high speed operation would result in a premature seizure because of deterioration of the grease under the influence of heat evolving in the bearing assembly and/or the lack of oil films in raceway surfaces, particularly the inner ring. Specifically, in a region of high speed revolution, in which the dn value exceeds 1,000,000 (bearing inner diameter (mm)×number of revolutions (rpm)), it is indeed difficult to ensure a grease operating life.
Some suggestions have been made to increase the grease operating life. One of them is the use of a grease reservoir in an outer ring raceway surface portion to ensure a long life at a high speed environment. (See, for example, the Japanese Laid-open Patent Publication No. H11-108068, published Apr. 20, 1999.) Another one of the suggestions is the use of a grease supply device provided outside a spindle so that a lubricant oil can be suitably supplied from such supply device to bearings. (See, for example, the Japanese Laid-open Patent Publication No. 2003-113998, published Apr. 18, 2003.)
It has, however, been found that the techniques hitherto suggested as hereinabove discussed are not considered satisfactory in respect of the number of revolutions used which is comparable with that in the air oil lubrication (dn value of more than 1.5 million), and/or the maintenance-free.
In view of the foregoing, the technique disclosed in the Japanese Laid-open Patent Publication No. H11-108068 is advanced in such a way that an axially extending minute gap is formed so as to communicate between a grease reservoir, which is defined in proximity to a stationary raceway ring (for example, an outer ring), and a portion in proximity to a raceway surface defined in the stationary raceway ring, a base oil within the grease reservoir is transferred to an area proximate to the raceway ring by the effect of a thickening agent and a capillary phenomenon occurring within the axially extending gap and then retained by the effect of a surface tension, and the base oil is eventually discharged, by the effects of a volumetric expansion of the base oil, which is caused as a result of an increase of the temperature in the axially extending gap during the operation, and of an airflow induced by a rotation of a rotatable raceway ring, so that the base oil is deposited on the raceway surface.
It has, however, been found that the system, in which the base oil is transferred to the axially extending gap by the effect of only the thickening agent and the capillary phenomenon taking place within the axially extending gap, does not give rise to a sufficient capability of transferring the base oil and, therefore, lubrication of the bearing assembly is not always sufficient.